This invention relates to a method of applying a liquid coating composition to a workpiece.
The application of a liquid coating composition by utilization of spraying apparatus such as a spray gun requires that said composition have physical characteristics which permit its atomization into liquid particles of effective size and uniformity. One major consideration in determining proper atomization concerns the viscosity of the composition, since high viscosity inhibits atomization. A paint composition having a high solids content exemplifies such a high viscosity coating composition whose physical characteristics at room temperature do not permit proper atomization. However, and as practiced in the art, heating such a coating composition reduces its viscosity and consequently enhances atomization properties to thereby permit utilization of spraying apparatus.
Effective application of an atomized liquid coating composition to a workpiece can be enhanced, as taught in the art, by imparting an electrical charge to the liquid particles produced by the atomization and having an electrically receptive workpiece as, for example, a workpiece which is electrically grounded. One manner of imparting such an electrostatic charge is to provide an induction charging electrode means to spraying apparatus whereby the liquid particles are inductively charged upon their formation. To achieve such induction charging, however, the liquid particles must possess a sufficient magnitude of electrical conductivity since, otherwise, little or no charging can occur. In a paint composition having a high solids content, the electrical conductivity is of a value generally lower than the value preferred for optimum induction charging.